In many applications, MEMS components must be operated under precisely defined environmental conditions. For this reason, for example micromechanical rotational rate sensors and acceleration sensors are enclosed in a protective gas and at a prespecified pressure. In practice, for this purpose a cap is mounted on the chip surface over the micromechanical sensor structure. In order to produce a reliable pressure-tight connection between the cap and the chip surface, in most cases a bonding method is used. As a rule, the capping takes place on the wafer level, i.e. before the separation of the components, the cap structures also still being situated in the wafer composite. Capping wafers are typically structured using a small number of manufacturing steps. For example, recesses are often made in the wafer surface that, after assembly, each form a hollow space over the micromechanical structure of a component. A standard silicon wafer is typically used as a capping wafer. The thickness of such a wafer is, given a diameter of 150 mm, between 500 and 650 μm, and given a diameter of 200 mm is approximately 750 μm. Thinner wafers cannot be used in standard semiconductor manufacturing lines, because they do not have sufficient mechanical stability.
As a rule, the wafer stack made up of the component wafer and the capping wafer is thinned after the mounting of the capping wafer and before the separation, in order to reduce the constructive height of the MEMS components capped in this way. In practice, this is accomplished by mechanical wear, using grinding. In order to produce very thin components such as those required in consumer electronics, both the component wafers and the capping wafers have to be thinned, which is very expensive. In addition, the mechanical wearing away of material always entails the risk that the mechanical structure of the components will be damaged.
German Patent No. DE 103 50 036 describes a method for separating very thin semiconductor chips produced within a functional layer on a wafer substrate. According to this method, underneath the functional layer hollow spaces are made in the substrate so that the functional layer remains connected to the substrate underneath the hollow spaces only via support points. Here, the separation of the semiconductor chips takes place in two steps. In a first step, the functional layer is structured in such a way that the individual semiconductor chips remain connected to the substrate, and held in the wafer composite, only via the support points. The semiconductor chips are not separated from the substrate, by breaking the support points, until the second step.